Indoor GPS: Why tech companies want to track you inside

This week Apple purchased WiFiSLAM, an "indoor GPS" company whose technology allows precise navigation inside buildings. Indoor GPS could make navigating shopping centers and airports easier, but Apple and other companies will have to implement it in a way that respects users' privacy.

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Indoor GPS would allow Apple's iPhone, and other devices, to give users detailed navigation in buildings. Here, a man looks at his iPhone's screen as he walks down a street in downtown Shanghai.

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Every modern phone has a GPS built in, and some sort of navigation service to give you directions on the highway. But as soon as you get out of the car, that service isn't much use -- you might be able to guide yourself to a store that's a block away, but as soon as you step indoors you're out of luck. GPS can't help you find your friends in a mall, or direct you to the correct gate at an airport.

But that might change soon. This week Apple purchased Silicon Valley start-up WiFiSLAM, an "indoor GPS" company whose technology can pinpoint a device's location indoors. Indoor GPS works by using Wi-Fi signals, as well as data from phone sensors like a compass and accelerometer, to enable much more precise tracking than is possible with regular GPS. The company says that it can peg a user's indoor location to within 2.5 meters, or about 8 feet.

So far, WiFiSLAM has been marketing its technology to app developers who want to be able to make indoor maps, according to Jessica Lessin at The Wall Street Journal. That might also allow for new kinds of retail apps -- picture what it would be like to have your phone give you sale information about whatever kind of produce you're standing in front of at the grocery store.

The purchase of WiFiSLAM is almost certainly a way for Apple to step up its mapping game against rival Google. Google Maps has included indoor navigation for a little while already, albeit only for buildings that the company has mapped already -- things like sports arenas and shopping centers. (Google says its database includes 10,000 buildings in 13 countries.) Apple, meanwhile, foundered initially as its own mapping service debuted last year to critical reviews. The company has since worked hard to improve Apple Maps, and WiFiSLAM could be a big step up -- for starters, since the technology relies partially on data from phone sensors, everyone using an iPhone indoors would be helping to create maps of the buildings they're in.

Indoor GPS, of course, raises some privacy concerns -- not least because it would allow Apple, or any other company that employs it, to collect pretty specific data on users' movements and habits. Since companies need to find a way to make money on services like this, it's probably not reasonable to expect a free indoor GPS that also completely respects users' privacy.